In this type of the exhaust gas measurement apparatus, as disclosed in Patent Literature 1, concentrations of various components contained in the exhaust gas discharged from an internal combustion engine are measured.
Especially, a CO concentration is varied largely in a short time in a range from a several ppm order to a percentage (%) order according to an operating condition of an engine and a warming-up state of a catalyst.
For example, in a state that a large amount of fuel is supplied and a catalyst is not yet sufficiently warmed, at a time of initial operation of the engine or the like, since there occurs an incomplete combustion and a catalytic function is not sufficiently exerted, CO gas produced by such as an incomplete combustion is discharged from a vehicle tailpipe of a vehicle without being oxidized to be CO2 by the catalyst. Therefore, the CO concentration at this time is extremely high. Meanwhile, in the case where the catalyst is warmed up, the CO component is almost oxidized to be CO2 by the catalyst and therefore the concentration of the CO component contained in the exhaust gas is reduced to be a few ppm order.
In this way, since a difference between a high concentration and a lower concentration of the CO component is large, the CO concentration has been conventionally measured by providing two types of CO concentration meters having, for example, different measurement ranges.
However, since it is necessary to use two types of the CO concentration meters, there is a problem that a maintenance cost and an initial investment cost are increased. Further, also in measurement accuracy, a correlation at a timing of switching between the two CO concentration meters becomes a problem of measurement accuracy in some cases.
Similar problems may also arise in measuring concentrations of the other components (for example, THC and the like) contained in the exhaust gas.